538 METALLURGY OF CAST IRON.
crease of strength of the i^ bars, which is displayed by test No. 7 being weaker than tests Nos. 4 and jo. This is due to the high sulphur in the iron when in a small body as of i^ inches diameter, causing the combined carbon to overreach its limit for gradually increasing the strength of the i^-inch bars, as shown by the break in tests Nos. i, 4, 10, 13, and 16. Test No. 7 is one which strongly emphasizes the wisdom of not using bars smaller than \% inches in diameter where the best comparative records are desired, and strongly endorses the A. F. A. recommendations, seen on page 577. The second factor is that shown by the low strength displayed by the '' Bessemer '' iron shown in Table 113. Had the " iron " in the Bessemer Table 113 been near the percentage seen in Table in, for heavy machinery, the strength of the test bars in Table 113 should have nearly equalled that of Table iii. To note the influence of " iron " on the strength of grades, see Table 37, page 250.